The present invention relates to a rolled paper sheet conveying apparatus of a plotter using a paper roll and a rolled paper conveying route control method.
Conventionally, a plotter using paper rolls of an automatic drafting machine is known. The important point of such plotter is that the rolled paper sheet is pulled out to a platen of the automatic drafting machine with a uniform tension on left and right edges of the sheet and rolled around a winding means with a uniform tension effective along the transverse direction of the sheet. Attaining such uniform tension on a sheet to be enables the sheet supplied to a correct and precise position on the platen.
In order to obtain a construction of the rolled paper conveying apparatus of the plotter enabling to attain uniform tension on both edges of the sheet, it has been necessary to manufacture respective parts and assemble them with high precision. This is because lengths of left and right conveying routes of the rolled paper must be equal to each other, and a drafting roller, a feeding roller (feeding means), and a winding roller (winding means) must be arranged in a three-dimensional parallel relation.
It is noted that it is very difficult to always obtain a high degree of precision in manufacturing the parts and assembling them with a reasonable cost. If high degree precision is attained in the parts and their assembly, it is very difficult to keep the precision for a long period of usage and in transportation of the plotter.
It has been found that when a predetermined range for one frame of the sheet paper in the plotter is made suspended, after a upon drawing the sheet paper, taking the sheet from the winding roller, by a feeding operation of a drive roller and winding the no-tensioned suspended sheet onto the winding roller, sheet winding error, generated from a small installation error of the winding roller and a front tension roller placed up-stream of the winding roller, can be controlled or diminished by a flange of the winding roller.
Feeding roller installation error can be solved by paying out a sheet part of the rolled paper through a feeding roller so as to make the sheet part slacken, and then pulling up the slackened sheet part onto the platen through the drive roller so as to convey the sheet correctly.
However, this conventional idea has the shortcoming as that only slackening the paper and pulling up it by the drive roller causes some snake-motion of the running sheet.
In order to prevent the running paper sheet from being snaked, the plotter has been provided with a set of tension rollers on its legs so as to give weak tension to the sheet placed at its feeding side. When the installation axis of the tension roller is not perfectly parallel to a Y-axis of the tension roller, it is difficult or impossible to precisely convey the paper sheet onto the platen.